In shipboard sleeping arrangements, and most particularly, on cruise ships, stateroom space is customarily very compact, generally to allow a maximum amount of room in the shipboard common areas, for entertainment, dining, sports facilities, etc. In fact, typically the furniture, plumbing fixtures, closets, etc. in shipboard staterooms very efficiently utilize the space allotted to the staterooms, often in having smaller-than-usual furniture, fixtures, etc.
In addition, stateroom beds, furniture and the like are generally fixedly mounted to the deck, bulkhead or the like, to prevent them from being tossed about as the result of the motion of the ship in response to weather, conditions of the sea, etc.
Because it is not known in advance what the booking needs of a given ship, especially a cruise ship, are going to be at the time that the ship is built, there is a tendency when ships are built to outfit staterooms with a pair of spaced-apart individual beds that are as small as, or generally smaller than conventional "single" size beds, rather than to outfit them with "double"-size beds, "queen"-size or "king"-size beds. The rational seems to be that customers who would prefer a common bed, such as a double bed, queen-size bed or a king-size bed can more readily be satisfied if they have to forego their preference and make do with separate beds, than can customers who want separate beds be satisfied if only a common bed is available for accommodating two people. This is especially understandable when one considers that the booking practices of most cruise lines is that, in the case of passengers traveling alone, such can or will be booked to share a room with a stranger, in order for such customer to avoid having to pay a cruise cost approaching that which would be charged for two people, as would be the case, for example, should a passenger insist upon not sharing a room.
There are many other reasons why passengers may prefer separate arrangements, as distinguished from common sleeping arrangements, or the converse. Such reasons can include people of substantial size desiring the comforts of a large, common bed, rather than small, separate beds, couples accustomed to sharing a common bed, people who do not care to share a bed with another person whether they are strangers or not, etc.